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jbeck26

1D Culvert Modeling

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I am developing several 1D TUFLOW models to simulate existing natural channels and then proposed conditions where a portion of the existing channel becomes replaced with a new box culvert.  Both the existing and proposed models have several culverts incorporated into them.

 

In my example, the actual culvert length is 80 feet while the culvert 1d channel segment between cross-sections is 100 feet.  The XS lines immediately downstream and upstream of the culverts are slightly beyond the each end of the culvert.  In this example, there is a 15’ difference on the left side and a 5’ difference on the right side. 

 

The actual culvert lengths were manually entered into the 1d_nwk attribute table; these lengths, however, will not match the channel length between the U/S XS and the D/S XS.  Does TUFLOW inherently account for this difference?  In other hydraulic modeling programs, you have to specify the distance from the culvert headwall to the adjacent XS – does the same apply for TUFLOW?  We want to make sure that TUFLOW is correctly calculating culvert losses based on the true length and that the extra sectional length between the start/end of the culvert and the adjacent XS is being accounted for.  If you could provide some insight into how TUFLOW handles this situation and performs calculations that would be appreciated and helpful for us to get a better understanding of the program so we can modify our models if needed.  We have several culverts in both the Rag Run and Poorhouse Run models so it is important we clarify this issue. 

 

In addition, I am curious as how TUFLOW uses the geographic location of the cross-sections and 1d_network channels.  Does TUFLOW use the XS data contained within the CSV files in combination with the specific locations of the XS lines to build the model?  Do the channel lengths in the 1d_nwk GIS attribute table have to match the actual length of the stream segment between consecutive cross-section lines? 

 

Any help would be greatly appreciated as we are relatively new at using TUFLOW.

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Hi,

 

If you omit a length in the 11d_nwk attibutes (or a length less than or equal to zero is used) then length of the channel is calculated based on the length of the GIS line.  If you specify a length in the attributes this will overwrite the GIS length.  If you have a length attribute specified on the culvert, but not on the upstream and downstream channels, the length on these will be based on the length of the GIS objects.  This would mean that there is a length of channel that is not being accounted for.  Typically In this situation, the length of the upstream and downstream channels would be specified to account for this length.  The channel length specified and the GIS length do not have to match, if specified the length attribute in the 1d_nwk overwrites the GIS length.

 

For cross-section locations, cross-sections can be input at either the ends of the channel or at the channel centre. A cross-section that is specified along the channel length (not at the end) is treated as a centre cross-section.  Multiple sections can not be specified along the one channel (Error 1123 is generated).

 

For some channels (for example bridges), it is necessary to specify a centre cross-section.  However, for the "S" type open channel, either method can be used.  There is more of a discussion on this in Section 4.6.4 of the TUFLOW manual.  If both end sections and a centre cross-section are specified for the same channel, the centre section is given priority and Warning 1152 is generated.

 

Hope this helps.

 

Let us know if you need any further info.

 

Cheers

Phil

 

 

 

 

 

 

 

 

 

 

 

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